This invention relates to drive arrangements for motor vehicles.
In order to reduce fuel consumption, it is known to turn off the engine of a motor vehicle and restart the engine again in accordance with particular operating conditions. When the engine is turned off, it is necessary to disconnect the drive train of the vehicle by at least one coupling. Turning off and restarting of the engine, as well as disconnection of the drive train coupling, are monitored by a special device such as an electronic control instrument, and are performed automatically. When this procedure is used in conjunction with a servo-supported, i.e., semiautomatic, stepped-gear transmission, relatively favorable fuel consumption can be obtained, particularly with variable driving conditions. This performance is obtained in part because, when the vehicle is coasting and the engine is turned off, the transmission floats in the idling condition, resulting in low friction losses. The use of a torque-converter automatic transmission, having a fluid coupling to provide greater comfort and a wider range of transmission ratios, has not been considered previously in connection with a motor-disconnecting coupling-transmission-driveshaft drive train because of its rather poor mechanical efficiency. This is because, with that arrangement, the coasting vehicle must drive the transmission with the engine turned off, causing friction or torque converter energy losses.